Ion implantation method and ion implanter

ABSTRACT

An ion implantation method includes irradiating a wafer having a first temperature with a first ion beam such that a predetermined channeling condition is satisfied and irradiating the wafer having a second temperature different from the first temperature with a second ion beam such that the predetermined channeling condition is satisfied, after the irradiation of the first ion beam.

RELATED APPLICATIONS

Priority is claimed to Japanese Patent Application No. 2018-135346,filed Jul. 18, 2018, the entire content of which is incorporated hereinby reference.

BACKGROUND Technical Field

Certain embodiment of the present invention relates to an ionimplantation method and an ion implanter.

Description of Related Art

In a semiconductor manufacturing process, in order to changeconductivity of a semiconductor and/or change a crystal structure of asemiconductor, a process of implanting ions into a semiconductor wafer(referred to as an ion implantation process) is generally performed. Theion implantation process may be performed via a mask formed on a wafersurface, and in this case, ions are selectively implanted at a locationcorresponding an opening region of the mask. Moreover, ions may beselectively implanted using an element structure such as a gateelectrode formed on the wafer surface, and in this case, ions areimplanted into a source/drain region or other device structure partadjacent to the gate electrode.

In addition, it is known that an aspect of an interaction between an ionbeam and the wafer is changed according to an implantation angle of theion beam with which the wafer is irradiated, which influences aprocessing result of ion implantation. Accordingly, it is required toaccurately control the implantation angle of the ion beam in order toobtain a desired implantation profile. For example, by controlling theimplantation angle of the ion beam such that a predetermined channelingcondition is satisfied, it is possible that the ions reach a deeperposition and a deeper implantation profile can be realized. Meanwhile,by controlling the implantation angle of the ion beam such that thechanneling condition is not satisfied, an implantation profile having adistribution which spreads in a horizontal direction at a shallowerposition can be realized.

SUMMARY

According to an embodiment of the present invention, there is providedan ion implantation method including: irradiating a wafer having a firsttemperature with a first ion beam such that a predetermined channelingcondition is satisfied; and irradiating the wafer having a secondtemperature different from the first temperature with a second ion beamsuch that the predetermined channeling condition is satisfied, after theirradiation of the first ion beam.

According to another embodiment of the present invention, there isprovided an ion implantation method including: heating or cooling awafer to a predetermined temperature using a temperature adjustmentdevice; irradiating the wafer having the predetermined temperature withan ion beam such that a predetermined channeling condition is satisfied;forming, compared to an implantation profile formed in the wafer whenthe wafer is irradiated with an ion beam such that the predeterminedchanneling condition is satisfied at a temperature different from thepredetermined temperature, a different implantation profile in the waferin at least one of a depth direction and an in-plane directionperpendicular to the depth direction.

According to still another embodiment of the present invention, there isprovided an ion implanter. The ion implanter includes a beamline deviceconfigured to transport an ion beam; a wafer holding device configuredto hold a wafer to be irradiated with the ion beam; and a temperatureadjustment device configured to heat or cool the wafer. The wafer isheated or cooled to a predetermined temperature using the temperatureadjustment device, the wafer is held by the wafer holding device suchthat a predetermined channeling condition is satisfied, and the waferhaving the predetermined temperature which is held by the wafer holdingdevice is irradiated with the ion beam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams schematically showing presence or absenceof a channeling phenomenon of an implanted ion.

FIGS. 2A and 2D are diagrams schematically showing angularcharacteristics of ion beams incident into a wafer and FIGS. 2E to 2Hare graphs schematically showing angular components of the ion beamscorresponding to FIGS. 2A to 2D.

FIG. 3 is a graph showing an example of a relationship between theimplantation angle of the ion beam and an implantation profile in adepth direction formed in the wafer.

FIG. 4 is a graph showing an example of a relationship between theimplantation angle of the ion beam and implantation concentrations attwo peak positions.

FIG. 5 is a graph schematically showing an example of a distribution ofthe implanted ions in the wafer.

FIG. 6 is a cross section schematically showing an example of a highenergy implantation process.

FIG. 7 is a graph showing an example of a relationship between a wafertemperature and the implantation profile in the depth direction formedin the wafer.

FIG. 8 is a graph showing an example of a relationship between the wafertemperature and implantation concentrations at two peak positions.

FIG. 9 is a graph showing an example of an implantation profile which isformed in the wafer when the wafer is irradiated with phosphorus (P)ions.

FIG. 10 is a graph showing an example of an implantation profile whichis formed in the wafer when the wafer is irradiated with arsenic (As)ions.

FIGS. 11A to 11C are cross sections schematically showing an example ofa multiple implantations according to an embodiment.

FIGS. 12A to 12C are cross sections schematically showing anotherexample of the multiple implantations according to the embodiment.

FIG. 13 is a top view showing a schematic configuration of an ionimplanter according to the embodiment.

FIGS. 14A and 14B are diagrams schematically showing a configuration ofa lens device included in a beam shaper.

FIG. 15 is a graph schematically showing an example of controlling aconvergence/divergence of the ion beam by the lens device.

FIG. 16 is a side view showing a configuration of a substratetransporting/processing unit in detail.

FIG. 17 is a side view schematically showing a process of disposing thewafer on a wafer holding device.

FIGS. 18A and 18B are diagrams schematically showing an orientation ofthe wafer with respect to an incident direction of the ion beam.

FIGS. 19A and 19B are diagrams schematically showing the wafer which isa target of an ion implantation process target.

FIGS. 20A to 20C are diagrams schematically showing a relationshipbetween the orientation of the wafer and an atomic arrangement in thevicinity of a surface of the wafer.

FIG. 21 is a flowchart showing a flow of an ion implantation methodaccording to the embodiment.

DETAILED DESCRIPTION

In a case where ions are implanted into a specific location of a wafersurface using a mask or other masking component, an implantation profilemay be changed according to an incident angle of an ion beam withrespect to a wafer surface, regardless of presence or absence ofchanneling. For example, if the beam is perpendicularly incident intothe wafer surface, the ions are implanted around a positionedimmediately below an opening region of the mask. However, if the beam isobliquely incident into the wafer surface, the ions are implanted arounda position obliquely offset from the opening region of the mask.Therefore, even if the implantation angle of the ion beam is strictlycontrolled, a desired implantation profile cannot always be formed at adesired position.

It is desirable to provide an ion implantation technology capable ofrealizing a desired implantation profile.

Aspects of the present invention include any combination of theabove-described elements and mutual substitution of elements orexpressions of the present invention among apparatuses, methods,systems, or the like.

According to the present invention, it is possible to provide an ionimplantation technology capable of realizing a desired implantationprofile.

Hereinafter, an embodiment of the present invention will be described indetail with reference to the drawings. In description of the drawings,the same reference numerals are assigned to the same elements, andrepeated descriptions will be omitted appropriately. Configurationsdescribed below are illustrative and do not limit the scope of thepresent invention.

Before the embodiment is described, an overview of the present inventionwill be described. In the ion implantation method according to thepresent embodiment, a wafer is heated or cooled to the predeterminedtemperature using a temperature adjustment device, and the wafer havinga predetermined temperature is irradiated with an ion beam such that apredetermined channeling condition is satisfied. Here, the expressionthat “a predetermined channeling condition is satisfied” means thatimplantation process is performed such that an angular condition of theion implantation is satisfied, which can cause a channeling phenomenonby getting the ion beam to be incident along a crystal axis or a crystalplane of the wafer. According to the present embodiment, it is possibleto form a desired implantation profile in the wafer by appropriatelycontrolling both the angular condition of the ion implantation and atemperature condition of the wafer during the ion implantation.

FIGS. 1A and 1B are diagrams schematically showing presence or absenceof a channeling phenomenon undergone by an implanted ion 92. FIG. 1Ashows an aspect in which the implanted ion 92 goes through an inside ofa crystal lattice 90. An incident angle θ₁ of the implanted ion 92 withrespect to a crystal axis C of the crystal lattice 90 is relativelysmall, and the implanted ion 92 travels inside of the crystal lattice 90along the crystal axis C. Therefore, an influence of interaction betweenthe implanted ion 92 and atoms 91 constituting the crystal lattice 90 issmall, and the implanted ion 92 can reach linearly to a deeper positionof the crystal lattice 90.

FIG. 1B shows an aspect in which the implanted ion 92 does not gothrough the inside of the crystal lattice 90. An incident angle θ₂ ofthe implanted ion 92 with respect to the crystal axis C of the crystallattice 90 is relatively large, and the implanted ion 92 travels insideof the crystal lattice 90 so as to intersect the crystal axis C,interacts with the atoms 91 constituting the crystal lattice 90, and isscattered while traveling. Accordingly, the implanted ion 92 reachesonly a shallower position of the crystal lattice 90, and can reach aposition shifted from an initial implantation position in a directionperpendicular to an implantation direction (an upward-downward directionof a paper surface of FIG. 1B or a direction perpendicular to the papersurface of FIG. 1B).

In the present specification, a situation shown in FIG. 1A is referredto as an “on-channeling”, and a situation shown in FIG. 1B is referredto as an “off-channeling”. Whether the implanted ion 92 incident intothe crystal lattice 90 is in the “on-channeling” or in the“off-channeling” is mainly determined by the incident angles θ of theimplanted ion 92. An incident angle which becomes a threshold betweenthe on-channeling and the off-channeling may be referred to as acritical angle θ_(c). For example, the critical angle θ_(c) can beexpressed by the following Expression (1)

$\begin{matrix}{\theta_{C} = \sqrt{\frac{Z_{1}Z_{2}e^{2}}{2\pi\varepsilon_{0}E_{1}d}}} & (1)\end{matrix}$

Here, Z₁ is an atomic number of the implanted ion, Z₂ is an atomicnumber of a material which is an implantation target, E₁ is energy ofthe implanted ion, and d is an atomic interval in a crystal of thematerial which is the implantation target. For example, in a case wherethe implanted ion is boron (B), the implantation target is silicon (Si),and the atomic interval d corresponding to a (100) plane of a siliconcrystal is used, the critical angle θ_(c) is approximately 3.5° if theimplantation energy E₁=100 keV, and the critical angle θ_(c) isapproximately 1.1° if the implantation energy E₁=1 MeV. In addition, ina case where the implanted ion is phosphorus (P) and the otherconditions are the same as those described above, the critical angle θis approximately 6.0° if implantation energy E₁=100 keV, and thecritical angle θ is approximately 1.9° if implantation energy E₁=1 MeV.

If the incident angle θ of the implanted ion is sufficiently small incomparison with the critical angles θ_(c) having the above-describedvalues (θ<θ_(c)), the ion is implanted in the situation of theon-channeling shown in FIG. 1A. Meanwhile, if the incident angle θ ofthe implanted ion is sufficiently large in comparison with the criticalangles θ having the above-described values (θ>θ_(c)), the ion isimplanted in the situation of the off-channeling shown in FIG. 1B.Accordingly, in a case where the wafer is irradiated with the ion beamand the implantation process is performed on the wafer, depending on theangular characteristic of the ion beam, a reaching depth, a spread in ahorizontal direction of the implanted ions constituting the ion beam, orthe like can be changed, and a shape of the “implantation profile” whichis a concentration distribution of the implanted ions in the wafer canbe changed. Accordingly, in the ion implantation process, an inclinationangle of the wafer with respect to a traveling direction of the ion beamis adjusted, and an implantation angle which is an average value ofentire beam incident into the wafer is controlled.

The angular characteristic of the ion beam incident into the waferincludes an angular distribution which is as an ion group constitutingthe ion beam, in addition to the incident angle which is the averagevalue of entire beam. Inmost cases, the ion beam incident into the waferis more or less divergent or convergent, and the ion group constitutingthe beam has the angular distribution with a certain spread. Even in acase where the incident angle which is the average value of entire beamis larger than the critical angle θ_(c), if angular components of someions are smaller than the critical angle θ_(c), the channelingphenomenon is take place for the some ions. Conversely, even in a casewhere the incident angle which is the average value of entire beam issmaller than the critical angle θ_(c), if angular components of someions are larger than the critical angle θ_(c), the some ions shows theoff-channeling.

FIGS. 2A to 2D are diagrams schematically showing an angularcharacteristic of an ion beam B incident into a wafer W. In the FIGS. 2Ato 2D, in order to simplify the explanation, a case where theorientation of the crystal axis C is perpendicular to a surface of thewafer W and an “off angle” of a wafer main surface is 0° is shown. Theoff angle of the wafer W which is actually used is not necessary to be0° exactly.

FIG. 2A shows a “parallel beam” in which the ion beam B is incident intothe wafer W to be parallel to the crystal axis C of the wafer W andalmost all of the ions constituting the ion beam B travel to be parallelto the crystal axis C. FIG. 2B is similar to FIG. 2A in that the ionbeam B is the parallel beam, but shows an “oblique incident beam” inwhich the incident angle of the ion beam B is oblique to the crystalaxis C. FIG. 2C shows a “divergent beam” in which a beam diameter of theion beam B increases toward the wafer W so that the ion beam diverges,and FIG. 2D shows a “convergent beam” in which the beam diameter of theion beam B decreases toward the wafer W so that the ion beam converges.Accordingly, the ion beam B may diverge or converge with respect to thetraveling direction as the entire beam, and the ion beam B has an“angular distribution” indicating a variation of angular components ofions, separately from the traveling direction as the entire beam.

FIGS. 2E to 2H are graphs schematically showing the angulardistributions of the ion beams B corresponding to FIGS. 2A to 2D,respectively. A vertical axis of each graph indicates the number of theions constituting the ion beam B, and a horizontal axis of each graphindicates the incident angles θ of the ion particles constituting theion beam B with respect to the crystal axis C. In each graph, a range inwhich an absolute value of the incident angle θ is smaller than thecritical angle θ_(c) is indicated as an on-channeling region C1, and arange in which the absolute value of the incident angle θ is larger thanthe critical angle θ_(c) is indicated as an off-channeling region C2.

In FIG. 2E, a center of the angular distribution of the ion beam B is0°, a spread of the angular distribution of the ion beam B is small, andthus, the entire angular distribution is included in the on-channelingregion C1. As a result, in FIG. 2E, the implanted ions, which are in theon-channeling, are dominant. Meanwhile, in FIG. 2F, the center of theangular distribution of the ion beam B is larger than the critical angleθ while the spread of the angular distribution of the ion beam B issmall, and thus, the entire angular distribution is included in theoff-channeling region C2. As a result, in FIG. 2F, the implanted ions,which are in the off-channeling, are dominant. In FIGS. 2G and 2H, thespread of the angular distribution of the ion beam B is large, thecenter of the angular distribution of the ion beam B is 0°, and thus,the entire angular distribution extends over both the on-channelingregion C1 and the off-channeling region C2. As a result, in FIGS. 2G and2H, both the on-channeling and the off-channeling are mixed. Moreover, amixing ratio of the on-channeling and the off-channeling is changedaccording to the center angle of the angular distribution and amagnitude of the spread.

FIG. 3 is a graph showing an example of a relationship between theimplantation angle θ of the ion beam B and the implantation profile in adepth direction formed in the wafer. FIG. 3 shows a simulation result ina case where the implanted ion is set to be boron (B), the implantationtarget is set to be the (100) plane of silicon (Si), and theimplantation energy is set to be 1.5 MeV. The critical angle θ_(c) basedon the Expression 1 is approximately 0.9°. The ion beam B is thedivergent beam as shown in FIG. 2C, and a magnitude of the divergentangle (standard deviation value) is about 0.4°. The implantation angle θof the ion beam B is set to be 0°, 0.2°, 0.5°, 1°, 2°, and 5°. Ingeneral, as the implantation angle θ is smaller, the implantationprofile is distributed at a deeper position (to the right of the graph).In most cases, the implantation profile has two peaks, that is, a firstpeak P1 positioned at a depth of approximately 2.2 μm and a second peakP2 positioned at a depth of approximately 3.1 μm. The first peak P1tends to be lower as the implantation angle θ is smaller and to behigher as the implantation angle θ is larger, and thus, the first peakP1 is considered to correspond to the implanted ion under theoff-channeling. Meanwhile, the second peak P2 tends to be higher as theimplantation angle θ is smaller and to be lower as the implantationangle θ is larger, and thus, the second peak P2 is considered tocorrespond to the implanted ion under the on-channeling.

FIG. 4 is a graph showing an example of a relationship between theimplantation angle θ of the ion beam B and the implantationconcentrations at the two peak positions P1 and P2, and corresponds tothe implantation profile shown in FIG. 3 . A broken line P1 indicatesthe implantation concentration at a depth d=2.2 μm corresponding to thefirst peak, and a solid line P2 indicates implantation concentration ata depth d=3.1 μm corresponding to the second peak. As shown in FIG. 4 ,the implantation concentration at the first peak P1 tends to be lower asthe implantation angle θ is smaller and to be higher as the implantationangle θ is larger. Meanwhile, the implantation concentration at thesecond peak P2 tends to be higher as the implantation angle θ is smallerand to be lower as the implantation angle θ is larger.

FIG. 5 is a graph schematically showing an example of a distribution ofthe implanted ions 92 in the wafer. FIG. 5 shows a calculation result bya simulation under the same implantation condition as that in FIG. 3 ,where the implanted ion is boron (B), the implantation target is the(100) plane of silicon (Si), implantation energy is 1.5 MeV, theimplantation angle θ of the ion beam B is 0°, and the magnitude of thedivergent angle of the ion beam B is approximately 0.4°. A vertical axisof the graph indicates a depth position from the surface of the wafer W,and a horizontal axis of the graph indicates a position in an in-planedirection parallel to the surface of the wafer W. In the example shownin FIG. 5 , the implanted ions 92 exist over a range of 2.0 μm to 3.5 μmin the depth. Ions 93 implanted at relatively deep positions areimplanted ions under the on-channeling, and exist only near a center inthe in-plane direction. Meanwhile, ions 94 implanted at relativelyshallow positions are implanted ions under the off-channeling, and aredistributed so as to spread to a position away from a central positionin the in-plane direction. Accordingly, it can be seen that theimplanted ions 93 and 94 under the on-channeling and the off-channelingrespectively have different distributions also in the in-plane directionperpendicular to the depth direction.

As described above, the shape of the implantation profile formed in thewafer W can be controlled by accurately controlling the implantationangle θ with respect to the crystal axis C of the wafer W. Inparticular, if an angular condition in which the on-channeling isdominant is selected, an implantation profile having a smaller spreadin-plane direction can be realized at a deeper position. Meanwhile, ifan angular condition in which the off-channeling is dominant isselected, an implantation profile having a larger spread in the in-planedirection can be realized at a shallower position. In addition, it ispossible to control the entire depth position of the all implanted ionsby changing the energy of the implanted ion.

However, depending on a target of an ion implantation process, it maynot be possible to optionally change the implantation angle θ in orderto control the implantation profile. In recent years, there has beencustomer demand for implanting ions at a deeper position from the wafersurface in the depth direction in order to further shrink device sizesand improve characteristics thereof. In this case, in order to implantions only in a specific region in the in-plane direction, a mask isformed on the wafer surface. Moreover, for example, high energy ionbeams having an energy of 100 keV or more, or 1 MeV or more are used toimplant the ions at deeper positions.

FIG. 6 is a cross section schematically showing an example of a highenergy ion implantation process, and shows an aspect in which the waferW is irradiated with the ion beam B through a mask 80 which is providedon the surface of the wafer W and has a large thickness t. As shown inFIG. 6 , in order to appropriately block the high energy ion beam B, themask 80 on the wafer surface needs to be formed thick, and as a result,an aspect ratio of an opening portion 82 of the mask 80 increases.Therefore, if the ion beam is incident into the wafer W obliquely to thesurface of the wafer W, the ion beam obliquely incident into the openingportion 82 is blocked at least partially by a side surface 81 or thelike of the opening portion 82 because the opening portion 82 has thehigh aspect ratio. Therefore, an implantation area 84 corresponding tothe opening portion 82 is difficult to be appropriately irradiated withthe ion beam. Thus, in a case where the mask 80 having the openingportion 82 with high aspect ratio is used, the ion beam B should beincident almost perpendicularly to the wafer W, and thus, the incidentangle θ of the ion beam B is restricted due to a mask configuration. Inthis case, the incident angle θ of the ion beam B cannot be optionallyset in order to control the implantation profile.

Therefore, the present inventors tried to control the shape of theimplantation profile formed in the wafer W by adjusting a temperaturecondition of the wafer W when the wafer is irradiated with the ion beamB. According to knowledge of the present inventors, by increasing thewafer temperature when the wafer W is irradiated with the ion beam B,the ions can be implanted under a situation in which the channeling isnot easy to occur relatively (that is, off-channeling tends to occur).Conversely, by decreasing the wafer temperature when the wafer isirradiated with the ion beam B, the ions can be implanted under asituation in which the channeling is easy to occur relatively (that is,on-channeling tends to occur).

FIG. 7 is a graph showing an example of a relationship between a wafertemperature T and the implantation profile in the depth direction formedin the wafer W. Similarly to FIG. 3 , FIG. 7 is a simulation result whenthe implanted ion is set to be boron (B), the implantation target is setto be the (100) plane of silicon (Si), the implantation energy is set tobe 1.5 MeV, and the divergent angle of the ion beam B is set to be 0.4°.Meanwhile, in FIG. 7 , the implantation angle θ of the ion beam B isfixed at 0°. The temperature T of the wafer W during the beamirradiation is set to be −273° C., −196° C., −100° C., 27° C., 150° C.,414° C. and 450° C. As shown in FIG. 7 , the implantation profiles aregenerally distributed at deeper positions (to the right of the graph) asthe wafer temperatures are lower. The first peak P1 of the implantationprofile tends to be smaller as the wafer temperature T is lower and tobe larger as the wafer temperature T is higher. Meanwhile, the secondpeak P2 of the implantation profile tends to be larger as the wafertemperature T is lower and to be smaller as the wafer temperature T ishigher.

FIG. 8 is a graph showing an example of a relationship between the wafertemperature T and the implantation concentrations at the two peakpositions P1 and P2 and corresponds to the implantation profiles shownin FIG. 7 . The broken line P1 indicates the implantation concentrationat a depth d=2.2 μm corresponding to the first peak, and the solid lineP2 indicates implantation concentration at a depth d=3.1 μmcorresponding to the second peak. As shown in FIG. 7 , the implantationconcentration at the first peak P1 tends to be lower as the wafertemperature T is lower and to be higher as the wafer temperature ishigher. Meanwhile, the implantation concentration at the second peak P2tends to be higher as the wafer temperature T is lower and to be loweras the wafer temperature is higher.

As described above, similarly to the case of changing the implantationangle θ, it is understood that the implantation profile can be changedby changing the wafer temperature T during the ion implantation.Specifically, by lowering the wafer temperature T, a state where theon-channeling is dominant can be realized. It is considered that this isbecause the channeling is easily occur when the temperature of the waferW is lowered, movements of atoms constituting the crystal lattice of thewafer W decrease, and a probability of an interaction between theimplanted ion and the crystal lattice of the wafer W decreases.Therefore, by lowering the wafer temperature T, it is possible torealize an implantation profile in which the spread in the in-planedirection is smaller at a deeper position. Meanwhile, by raising thewafer temperature T, a state where the off-channeling is dominant isrealized, and thus, it is possible to realize an implantation profile inwhich the spread in the in-plane direction is larger at a shallowerposition.

In the present embodiment, the wafer W is heated or cooled to apredetermined temperature, and the wafer W having the predeterminedtemperature is irradiated with the ion beam B such that a predeterminedchanneling condition is satisfied. As a result, an implantation profileis realized, which is different from the implantation profile which isrealized when the wafer W is irradiated with the ion beam B such thatthe predetermined channeling condition is satisfied at a temperaturedifferent from the predetermined temperature. For example, compared witha case where the wafer W is irradiated with the ion beam B at the roomtemperature (27° C.), in a case where the wafer W is irradiated with theion beam B at a temperature lower than the room temperature, it ispossible to realize an implantation profile in which the spread in thein-plane direction is smaller at a deeper position. Compared with a casewhere the wafer W is irradiated with the ion beam B at the roomtemperature, in a case where the wafer W is irradiated with the ion beamB at a temperature higher than the room temperature, it is possible torealize an implantation profile in which the spread in the in-planedirection is larger at a shallower position.

Here, it is repeated that the term “predetermined channeling condition”refers to the condition of the implantation angle θ in which theon-channeling is dominant under the room temperature condition, and forexample, refers to the condition in which many of the angular componentsof the irradiating ion beam B are within the range of the critical angleθ which is calculated by Expression (1). As an example, the case wherethe predetermined channeling condition is satisfied is a case where atleast a full width at half maximum of the angular distribution of theirradiating ion beam B is included in the on-channeling region C1.

For example, the ion implantation method according to the presentembodiment can be applied to an isolation implantation or a photodiodeimplantation when a CMOS image sensor is manufactured. In the isolationimplantation, for example, the above-described boron (B) can be used asan implant species, and in the photodiode implantation, phosphorus (P)or arsenic (As) can be used. The present embodiment can be applied a tohigh energy implantation, and the implantation energy of the high energyimplantation can be set to be 200 keV to 20 MeV, for example. In thiscase, an implantation depth which can be realized is approximately 0.1μm to 10 μm.

In a case where the implantation target is the (100) plane of silicon(Si), the critical angle θ based on the Expression (1) of boron (B),phosphorus (P), and arsenic (As) according to the implantation energy isas follows. In a case where the implantation energy is 200 keV, thecritical angle θ_(c) of boron (B) is 2.47°, and the critical angle θ_(c)of phosphorus (P) is 4.27°, the critical angle θ of arsenic (As) is6.34°. In a case where the implantation energy is 2 MeV, the criticalangle θ_(c) of boron (B) is 0.78°, the critical angle θ_(c) ofphosphorus (P) is 1.35°, and the critical angle θ_(c) of arsenic (As) is2.00°. In a case where the implantation energy is 10 MeV, the criticalangle θ_(c) of boron (B) is 0.35°, the critical angle θ_(c) ofphosphorus (P) is 0.60°, and the critical angle θ_(c) of arsenic (As) is0.90°. As described above, the critical angle θ_(c) which provides theon-channeling depends on the ion species and the implantation energy,and thus, it is preferable to set an appropriate angular condition ofthe ion beam B according to the implantation condition. For example, theangular condition of the ion beam B corresponding to the predeterminedchanneling condition can be within 7°, within 5°, within 3°, or within1° with respect to the crystal axis C.

FIG. 9 is a graph showing an example of the implantation profile whichis formed in the wafer when the wafer is irradiated with phosphorus (P)ions. FIG. 9 is a graph showing a measurement result by Secondary IonMass Spectrometry (SIMS). The implantation target is the (100) plane ofsilicon (Si), and the implantation energy is 2.2 MeV. As shown in FIG. 9, in a case where the implantation angle θ is 0° and the wafertemperature T is the room temperature (27° C.), the effect of theon-channeling is noticeable, and the implantation profile has a highimplantation concentration which does not change largely over a depthrange of 2 μm to 4 μm. Meanwhile, in a case where the wafer temperatureT is a high temperature (450° C.) in a state where the implantationangle θ is 0°, or in a case where the implantation angle θ is 1° or 2°in a state where the wafer temperature T is the room temperature (27°C.), the implantation profile is formed, in which while there is a peakat a depth of approximately 2 μm under the off-channeling, theimplantation concentration is low at a depth of approximately 3 μm to 4μm. Therefore, also in a case where phosphorus (P) is implanted, byraising the wafer temperature T in a state where the implantation angleθ is fixed to be approximately 0°, it is possible to realize theimplantation profile similar to the implantation profile obtained in acase where the implantation angle θ is set to be approximately thecritical angle (for example, 1.29°) and the wafer temperature T is setto be the room temperature.

FIG. 10 is a graph showing an example of the implantation profile whichis formed in the wafer when the wafer is irradiated with arsenic (As)ions. FIG. 10 is a graph showing a measurement result by SIMS. Theimplantation target is the (100) plane of silicon (Si), and theimplantation energy is 3.1 MeV. As shown in FIG. 10 , in a case wherethe implantation angle θ is 0° and the wafer temperature T is the roomtemperature (27° C.), due to the effect of the on-channeling, theimplantation profile is obtained in which the implantation concentrationgently decreases over a range from the peak position having a depth ofapproximately 2 μm to a depth of approximately 6 μm. Meanwhile, in acase where the wafer temperature T is a high temperature (450° C.) in astate where the implantation angle θ is 0°, or in a case where theimplantation angle θ is 1° or 2° in a state where the wafer temperatureT is the room temperature (27° C.), the implantation profile is formed,in which there is a more prominent peak at a depth of approximately 2 μmunder the off-channeling and thus, the implantation concentration moresignificantly decreases in a range of approximately 2 μm or more in thedepth. Therefore, also in a case where arsenic (As) is implanted, byraising the wafer temperature T in a state where the implantation angleθ is fixed to be approximately 0°, it is possible to realize theimplantation profile similar to the implantation profile obtained in acase where the implantation angle θ is set to be approximately thecritical angle (for example, 1.61°) and the wafer temperature T is setto be the room temperature.

The present method can be applied to ion species other than B, P, andAs, and for example, can be applied to nitrogen (N), aluminum (Al),gallium (Ga), indium (In), antimony (Sb), or the like.

In the method according to the present embodiment, it is preferable toset a dose of the irradiating ion beam B to be an approximately mediumor less, and for example, preferably, the dose is 1×10¹⁴ cm⁻² or less,or 1×10¹³ cm⁻² or less. If the dose increases too much, implantationdamage is accumulated in a region irradiated with the beam by the ionimplantation process, the crystal structure becomes amorphous, and thecrystal state is changed to a state in which the channeling is difficultto occur.

The present embodiment can be also applied to multiple implantations inwhich the same implantation region in the wafer surface is irradiatedwith the ion beams having different implantation energies. For example,the same implantation region is irradiated with three ion beams havinghigh energy, medium energy, and low energy, the ions are implanted inthree ranges which centers respectively correspond to three differentdepth positions, and thus, it is possible to form an implantationprofile in which a region having a high implantation concentration iscontinuous in the depth direction. In this case, by performing themultiple implantations while changing the wafer temperature T, it ispossible to more accurately control the shape of at least one of theimplantation profiles in the depth direction and the implantationprofile in the in-plane direction.

FIGS. 11A to 11C are cross sections schematically showing an example ofa multiple implantations according to an embodiment. First, in a firstprocess of FIG. 11A, a relatively deep first portion 86 a in theimplantation region corresponding to the opening portion 82 of the mask80 is irradiated with a first ion beam B11 having high energy.Subsequently, in a second process of FIG. 11B, a second portion 86 bpositioned at an approximately medium depth in the implantation regioncorresponding to the opening portion 82 of the mask 80 is irradiatedwith a second ion beam B12 having medium energy. Thereafter, in a thirdprocess of FIG. 11C, a relatively shallow third portion 86 c in theimplantation region corresponding to the opening portion 82 of the mask80 is irradiated with a third ion beam B13 having low energy.Accordingly, an implantation region 86 in which the first portion 86 a,the second portion 86 b, and the third portion 86 c are continuous inthe depth direction is formed.

The implantation angles of the irradiating ion beams B11 to B13 in thefirst process to the third process respectively shown in FIGS. 11A to11C are the same, and the ion beams are approximately perpendicularlyincident into the wafer surface such that a predetermined channelingcondition is satisfied. Meanwhile, the wafer temperature T is changed ineach of the first process to the third process. In the first process, bysetting the wafer temperature T to be relatively low, the implantationcondition in which the on-channeling is dominant is realized, and awidth w₁ of the first portion 86 a in the in-plane direction is small.In the second process, by setting the wafer temperature T to be medium,the contribution of the off-channeling increases, and a width w₂ of thesecond portion 86 b in the in-plane direction is larger than the widthw₁ of the first portion 86 a. In the third process, by setting the wafertemperature T to be relatively high, the contribution of theoff-channeling further increases, and a width w₃ of the third portion 86c in the in-plane direction is larger than the width w₂ of the secondportion 86 b. In this way, by performing the implantation process of thefirst process to the third process while changing the temperatureconditions of the wafer, it is possible to form a trapezoidalimplantation region 86 in which the widths w₃ to w₁ in the in-planedirection decrease in order as getting away from the wafer surface (thatis, the implantation position gets deeper). Such a trench-typeimplantation profile can be used, for example as an isolationimplantation region.

FIGS. 12A to 12C are cross sections schematically showing anotherexample of the multiple implantations according to the embodiment.Similarly to FIGS. 11A to 11C, also in the example of FIGS. 12A to 12C,the portion corresponding to the opening portion 82 of the mask 80 isirradiated with ion beams B21 to B23 having different energies. First, afirst portion 88 a positioned at a relatively deep position isirradiated with the first ion beam B21 having high energy in a firstprocess of FIG. 12A, then, a second portion 88 b having an approximatelymedium depth is irradiated with the second ion beam B22 having mediumenergy in a second process of FIG. 12B, and at the last, a third portion88 c positioned at a relatively shallow position is irradiated with thethird ion beam B23 having low energy in a third process of FIG. 12C.Accordingly, an implantation region 88 in which the first portion 88 a,the second portion 88 b, and the third portion 88 c are continuous inthe depth direction is formed.

Meanwhile, temperature conditions of the wafer W of the example shown inFIGS. 12A to 12C are changed reversely to the above-describedtemperature conditions of the wafer W in FIGS. 11A to 11C. Specifically,in the first process, by setting the wafer temperature T to berelatively high, the implantation condition in which the off-channelingis dominant is realized, and the width w₁ of the first portion 88 a inthe in-plane direction is large. In the second process, by setting thewafer temperature T to be medium, the contribution of the on-channelingcontribution increases, and the width w₂ of the second portion 88 b inthe in-plane direction is smaller than the width w₁ of the first portion88 a. In the third process, by setting the wafer temperature T to berelatively low, the contribution of the on-channeling further increases,and the width w₃ of the third portion 88 c in the in-plane direction issmaller than the width w₂ of the second portion 88 b. In this way, byperforming the implantation process of the first process to the thirdprocess while changing the temperature conditions of the wafer, it ispossible to form the implantation region 88 having the shape in whichthe widths w₃ to w₁ in the in-plane direction increase in order asgetting away from the wafer surface (that is, the implantation positiongets deeper). Such another trench-type implantation profile can be used,for example, as a photodiode implantation region adjacent to theisolation implantation region 86 shown in FIG. 11C.

In the above-described examples, the number of the processes of themulti-stage implantations is three. However, the number of the processesof the multiple implantations may be two or four or more. In addition,only the wafer temperature T and the implantation energy may be changedin a state where the implantation angle of the irradiating ion beam inthe multiple implantations is fixed, and the implantation angle may bechanged between the processes.

In a case where the wafer temperature is changed, for example, it ispossible to change the temperature within a range of −200° C. to 500° C.By setting the change range of the temperature to be the range of −100°C. to 400° C., it is possible to adjust the temperature T of the waferusing a relatively simple temperature adjustment device. In a case wherethe wafer temperature T is changed between the processes of the multipleimplantations, it is preferable to set the temperature differencebetween processes to be 50° C. or more. By changing the wafertemperature T by 50° C. or more, preferably by 100° C. or more, a ratioof contributions of the on-channeling and the off-channeling occurringin a single implantation process can be significantly changed, and thus,it is possible to adjust the shape of the implantation profile in thedepth direction and the in-plane direction such that a desiredimplantation profile is obtained.

Subsequently, an ion implanter for performing the above-described ionimplantation method will be described.

FIG. 13 is a top view schematically showing an ion implanter 100according to the embodiment. The ion implanter 100 is a so-called highenergy ion implanter. The high energy ion implanter is an ion implanterhaving a radio frequency linear acceleration-type ion accelerator and abeamline for transporting high energy ions, and the high energy ionimplanter accelerates ions generated by an ion source 10, transports theobtained ion beam B to a processing object (for example, substrate orwafer W) along the beamline, and implants the ions into the processingobject.

The high energy ion implanter 100 includes an ion beam generation unit12 which generates ions and perform mass separation of the ions, a highenergy multiple linear acceleration unit 14 which accelerates the ionbeam to obtain a high energy ion beam, a beam deflection unit 16 whichperforms an energy analysis, an energy dispersion control, and atrajectory correction of the high energy ion beam, a beam transport lineunit 18 which transports the analyzed high energy ion beam to the waferW, and a substrate transporting/processing unit 20 which implants thetransported high energy ion beam into a semiconductor wafer.

The ion beam generation unit 12 has the ion source 10, an extractionelectrode 11, and a mass analyzer 22. In the ion beam generation unit12, a beam is extracted from the ion source 10 through the extractionelectrode 11 and simultaneously accelerated, and the extracted andaccelerated beam is mass-analyzed by the mass analyzer 22. The massanalyzer 22 has a mass analyzing magnet 22 a and a mass analyzing slit22 b. The mass analyzing slit 22 b may be disposed immediately behindthe mass analyzing magnet 22 a. However, in the embodiment, the massanalyzing slit 22 b is disposed in an entrance of the high energymultistage linear acceleration unit 14 which is the followingconfiguration. As a result of the mass analysis by the mass analyzer 22,only ion species necessary for the implantation is selected, and the ionbeam of the selected ion species is introduced to the following highenergy multistage linear acceleration unit 14.

The high energy multistage linear acceleration unit 14 includes aplurality of linear accelerator which performs the acceleration of theion beam, that is, one or more radio frequency resonators. The highenergy multistage linear acceleration unit 14 can accelerate the ions byan action of a radio frequency (RF) electric field. The high energymultistage linear acceleration unit 14 includes a first linearacceleration unit 15 a having a standard multistage of radio frequencyresonators for high energy ion implantation. The high energy multistagelinear acceleration unit 14 may additionally include a second linearacceleration unit 15 b having an additional multistage of radiofrequency resonators for ultra-high energy ion implantation. A directionof the ion beam which is further accelerated by the high energymultistage linear acceleration unit 14 is changed by the beam deflectionunit 16.

The high energy ion beam, which exits from the radio frequency-type highenergy multistage linear acceleration unit 14 which accelerates the ionbeam to high energy, has a certain range of energy distribution.Therefore, in order to perform beam scanning and beam parallelization onthe high energy ion beam in a downstream side of the high energymultistage linear acceleration unit 14 so as to irradiate the wafer withthe ion beam, it is necessary to perform a high accuracy energyanalysis, the trajectory correction, and adjustment of a beamconvergence/divergence in advance.

The beam deflection unit 16 performs the energy analysis, the energydispersion control, and the trajectory correction of the high energy ionbeam. The beam deflection unit 16 includes at least two high accuracydeflecting electromagnets, at least one energy width limiting slit, atleast one energy analyzing slit, and at least one horizontally focusingdevice. The plurality of deflecting electromagnets are configured toperform the energy analysis and the accurate ion implantation anglecorrection of the high energy ion beam.

The beam deflection unit 16 has an energy analyzing electromagnet 24, ahorizontally focusing quadrupole lens 26 for suppressing energydispersion, an energy analyzing slit 28, and a deflecting electromagnet30 for providing beam steering (trajectory correction). The energyanalyzing electromagnet 24 may also be referred to as an energy filterelectromagnet (EFM). The direction of the high energy ion beam is turnedby the beam deflection unit 16 and the high energy ion beam heads towardthe wafer W.

The beam transport line unit 18 is a beamline device which transportsthe ion beam B exiting from the beam deflection unit 16 and the beamtransport line unit 18 includes a beam shaper 32 constituted by afocusing/defocusing lens group, a beam scanner 34, a beam parallelizer36, and a final energy filter 38 (including a final energy separatingslit). A length of the beam transport line unit 18 is designed to matcha combined length of the ion beam generation unit 12 and the high energymultistage linear acceleration unit 14. The beam transport line unit 18and the high energy multistage linear acceleration unit 14 are connectedby the beam deflection unit 16 to form an entire U-shaped layout.

A substrate transporting/processing unit 20 is provided on a downstreamend of the beam transport line unit 18. The substratetransporting/processing unit 20 includes an ion implantation chamber 60and a substrate transfer unit 62. The ion implantation chamber 60includes a platen driving unit 40 which holds the wafer W during the ionimplantation and moves the wafer W in a direction perpendicular to abeam scanning direction. The platen driving unit 40 includes atemperature adjustment device 50 for adjusting the wafer temperature Tduring the ion implantation. In the substrate transfer unit 62, a wafertransfer mechanism such as a transfer robot which loads the wafer Wbefore the ion implantation into the ion implantation chamber 60 andunloads the wafer W subjected to the ion implantation from the ionimplantation chamber 60 is provided.

A beamline portion of the ion implanter 100 is constituted as ahorizontally folded U-shaped beamline having two long straight portionsfacing each other. An upstream long straight portion is constituted by aplurality of units which accelerate the ion beam B generated by the ionbeam generation unit 12. A downstream long straight portion is turnedwith respect to the upstream long straight portion and constituted by aplurality of units which adjust the ion beam B t and implant theadjusted ion beam B into the wafer W. The two long straight portions areconfigured to have substantially the same length. A workspace R1 havinga sufficient area for a maintenance work is provided between the twolong straight portions.

FIGS. 14A and 14B are diagrams schematically showing configurations oflens devices 32 a, 32 b, and 32 c included in the beam shaper 32. Forexample, the beam shaper 32 shown in FIG. 13 includes three quadrupolelens devices 32 a to 32 c, and the first lens device 32 a, the secondlens device 32 b, and the third lens device 32 c are disposed in thisorder from an upstream side toward a downstream side of a beamtrajectory. FIG. 14A shows the configurations of the first lens device32 a and the third lens device 32 c which focus the ion beam B in avertical direction (y direction), and FIG. 14B shows the configurationof the second lens device 32 b which focuses the ion beam B in ahorizontal direction (x direction).

The first lens device 32 a of FIG. 14A has a pair of horizontally facingelectrodes 72 which faces each other in the horizontal direction (xdirection) and a pair of vertically facing electrodes 74 which faceseach other in the vertical direction (y direction). A negative potential−Qy is applied to the pair of horizontally facing electrodes 72, and apositive potential +Qy is applied to the pair of vertically facingelectrodes 74. The first lens device 32 a generates an attractive forcefor an ion beam B, which is constituted as an ion group having positivecharge, between the pair of horizontally facing electrodes 72 having thenegative potential, and generates a repulsive force for the ion beam Bbetween the pair of vertically facing electrodes 74 having the positivepotential. Accordingly, the first lens device 32 a adjusts the beamshape so as to defocus the ion beam B in the x direction and focus theion beam B in the y direction. The third lens device 32 c is configuredin the same manner as the first lens device 32 a, and the samepotentials as the first lens device 32 a are applied to the third lensdevice 32 c.

The second lens device 32 b of FIG. 14B has a pair of horizontallyfacing electrodes 76 which faces each other in the horizontal direction(x direction) and a pair of vertically facing electrodes 78 which faceseach other in the vertical direction (y direction). While the secondlens device 32 b is configured in the same manner as the first lensdevice 32 a, the positive and the negative of the applied potentials arereversed. A positive potential +Qx is applied to the pair ofhorizontally facing electrodes 76, and a negative potential −Qx isapplied to the pair of vertically facing electrodes 78. The second lensdevice 32 b generates a repulsive force for the ion beam B, which isconstituted as the ion group having positive charges, between the pairof horizontally facing electrodes 76 having the positive potential, andgenerates an attractive force for the ion beam B between the pair ofvertically facing electrodes 78 having the negative potential.Accordingly, the second lens device 32 b adjusts the beam shape so as tofocus the ion beam B in the x direction and defocus the ion beam B inthe y direction.

FIG. 15 is a graph schematically showing an example of controlling aconvergence/divergence of the ion beams B by the lens devices 32 a to 32c, and shows a relationship between potentials Qx and Qy applied to thefacing electrodes of each of the lens devices 32 a to 32 c and anangular distribution of the shaped beam. A vertically focusing potentialQy on a horizontal axis indicates an absolute value of the potentialapplied to each of the first lens device 32 a and the third lens device32 c, and a horizontally focusing potential Qx on a vertical axisindicates an absolute value of the potential applied to the second lensdevice 32 b.

A point S at which predetermined potentials Qx₀ and Qy₀ are appliedmeans an operation condition which generates the “parallel beam” inwhich the spreads in implantation angle distributions in both the xdirection and the y direction are small as shown in FIGS. 2A and 2B. Bychanging the potentials Qx₀ and Qy₀ along a straight line Lx from thepoint S, it is possible to adjust the beam such that only theimplantation angle distribution in the x direction is changed and theimplantation angle distribution in the y direction is not changed. Ifthe horizontally focusing potential Qx is raised from the point S to apoint X1, the beam becomes a “convergent beam” which is convergent inthe x direction, and thus, the spread of the implantation angledistribution in the x direction increases. Meanwhile, if thehorizontally focusing potential Qx is lowered from the point S to apoint X2, the beam becomes a “divergent beam” which is divergent in thex direction, and thus, the spread of the implantation angle distributionin the x direction increases.

Similarly, by changing the potentials Qx and Qy along a straight line Lyfrom the point S, it is possible to adjust the beam such that only theimplantation angle distribution in the y direction is changed and theimplantation angle distribution in the x direction is not changed. Ifthe vertically focusing potential Qy is raised from the point S to apoint Y1, the beam becomes a “convergent beam” which is convergent inthe y direction, and thus, the spread of the implantation angledistribution in the y direction increases. Meanwhile, if the verticallyfocusing potential Qy is lowered from the point S to a point Y2, thebeam becomes a “divergent beam” which is divergent in the y direction,and thus, the spread of the implantation angle distribution in the ydirection increases.

In this way, by changing the potentials Qx and Qy applied to each of thethree-stage lens devices 32 a to 32 c under a predetermined condition,the implantation angle distributions in the x direction and the ydirection of the irradiating ion beam for the wafer W can be controlledindependently. For example, in a case where only the implantation angledistribution in the x direction is to be adjusted, the potentials Qx andQy maybe changed in accordance with an inclination of the straight lineLx such that a relationship of ΔQx=α·ΔQy is maintained. Similarly, in acase where only the implantation angle distribution in the y directionis to be adjusted, the potentials Qx and Qy may be changed in accordancewith an inclination of the straight line Ly such that a relationship ofΔQx=β·ΔQy is maintained. The values of the inclinations α and β of thestraight lines Lx and Ly may be appropriately determined according toion beam optical characteristics of the lens device used. In the presentembodiment, the angular distribution of the ion beam B can becontrolled, for example, with an accuracy of 0.1° or less.

FIG. 16 is a side view showing a configuration of the substratetransporting/processing unit 20 in detail and shows a configuration on adownstream side of the final energy filter 38. The ion beam B isdeflected downward through Angular Energy Filter (AEF) electrodes 64 ofthe final energy filter 38 and is incident into the substratetransporting/processing unit 20. The substrate transporting/processingunit 20 includes an ion implantation chamber 60 in which the ionimplantation process is performed and a substrate transfer unit 62 inwhich a transfer mechanism for transferring the wafer W is provided. Theion implantation chamber 60 and the substrate transfer unit 62 areconnected to each other via a substrate transfer port 61.

The ion implantation chamber 60 includes the platen driving unit 40which holds one or more wafer W. The platen driving unit 40 includes awafer holding device 42, a reciprocating motion mechanism 44, a twistangle adjustment mechanism 46, and a tilt angle adjustment mechanism 48.The wafer holding device 42 includes an electrostatic chuck or the likefor holding the wafer W. The reciprocating motion mechanism 44reciprocates the wafer holding device 42 in a reciprocating direction (ydirection) perpendicular to a beam scanning direction (x direction), andthus, the wafer W which is held by the wafer holding device 42 isreciprocated in the y direction. In FIG. 16 , a reciprocating motion ofthe wafer W is exemplified by an arrow Y.

The twist angle adjustment mechanism 46 is a mechanism which adjusts arotation angle of the wafer W, and rotates the wafer W with a normal ofa wafer processing surface as a rotation axis so as to adjust a twistangle between an alignment mark provided on an outer peripheral portionof the wafer and a reference position. Here, the alignment mark of thewafer means a notch, an orientation flat, or the like which is providedon the outer peripheral portion of the wafer, and means a mark servingas a reference for an angular position in a crystal axis direction ofthe wafer or in a circumferential direction of the wafer. The twistangle adjustment mechanism 46 is provided between the wafer holdingdevice 42 and the reciprocating motion mechanism 44, and is reciprocatedtogether with the wafer holding device 42.

The tilt angle adjustment mechanism 48 is a mechanism which adjusts theinclination of the wafer W, and adjusts a tilt angle between thetraveling direction (z direction) of the ion beam B toward the waferprocessing surface and the normal of the wafer processing surface. Inthe present embodiment, among the inclination angles of the wafer W, anangle with an axis in the x direction as a central axis of the rotationis adjusted as the tilt angle. The tilt angle adjustment mechanism 48 isprovided between the reciprocating motion mechanism 44 and a side wallof the ion implantation chamber 60 and is configured to adjust the tiltangle of the wafer W by rotating the entire platen driving unit 40including the reciprocating motion mechanism 44 in an R direction.

In the ion implantation chamber 60, an energy defining slit 66, a plasmashower device 68, and a beam damper 63 are provided along the trajectoryof the ion beam B from the upstream side toward the downstream side.

The energy defining slit 66 is provided on a downstream side of the AEFelectrodes 64 and performs an energy analysis of the ion beam B to beincident into the wafer W together with the AEF electrodes 64. Theenergy defining slit 66 is an Energy Defining Slit (EDS) configured of aslit long in the beam scanning direction (x direction). The energydefining slit 66 causes the ion beams having a desired energy value or adesired energy range to pass toward the wafer W and block the otherions.

The plasma shower device 68 is positioned on a downstream side of theenergy defining slit 66. The plasma shower device 68 supplies low energyelectrons to the ion beam B and the wafer processing surface incorresponding to a beam current of the ion beam B, and suppressescharge-up due to positive charge accumulated on the wafer processingsurface which result from the ion implantation. the plasma shower device68 includes, for example, a shower tube through which the ion beam Bpasses and a plasma generating device which supplies electrons into theshower tube.

The beam damper 63 is provided on the most downstream side of the beamtrajectory, and for example, is attached below the substrate transferport 61. Accordingly, in a case where the wafer W does not exist on thebeam trajectory, the ion beam B is incident into the beam damper 63. Abeam measuring device for measuring the ion beam B may be provided inthe beam damper 63.

The temperature adjustment device 50 is attached to the wafer holdingdevice 42 included in the platen driving unit 40. The temperatureadjustment device 50 heats or cools the wafer W, which is held by thewafer holding device 42, so as to adjust the temperature T of the waferW. The temperature adjustment device 50 includes at least one of aheating unit and a cooling unit. For example, the heating unit includesa heating wire, causes a current to flow through the heating wire so asto heat the heating wire, and thus, heats the wafer W. For example, thecooling unit includes a cooling flow path through which a refrigerantflows, and cools the wafer W by the refrigerant flowing through thecooling flow path. The temperature adjustment device 50 may include atemperature meter for measuring the temperature T of the wafer W and mayheat or cool the wafer W such that the temperature of the wafer Wmeasured by the temperature meter becomes a desired temperature.

The temperature adjustment device 50 may be provided at a positiondifferent from that of the wafer holding device 42. For example, aheating element may be disposed in the vicinity of an exit of the plasmashower device 68 and the wafer W may be heated using radiant heat fromthe heating element. The temperature adjustment device 50 may beprovided in middle of the wafer transfer path leading to the ionimplantation chamber 60 or may be provided in a preliminary chamberdifferent from the ion implantation chamber 60. The temperature of thewafer W may be adjusted by using both the temperature adjustment device50 provided in the wafer holding device 42 and another temperatureadjustment device provided at a position different from that of thewafer holding device 42.

FIG. 17 is a side view schematically showing a process of loading awafer W′ on the wafer holding device 42. In FIG. 17 , a solid lineindicates the wafer W′ which is disposed at a loading/unloading positionat which the wafer is loaded and unloaded between the wafer holdingdevice 42 and the substrate transfer unit 62, and a broken lineindicates the wafer W which is disposed at the implantation position atwhich the wafer is irradiated with the ion beam B inside the ionimplantation chamber 60. The platen driving unit 40 moves the wafers Wand W′ between the implantation position and the loading/unloadingposition mainly by a combination of a rotating movement in the Rdirection by the tilt angle adjustment mechanism 48 and a linearmovement in the Y direction by the reciprocating motion mechanism 44.The wafer W′ positioned at the loading/unloading position is loaded andunloaded through the substrate transfer port 61 by a substrate transferrobot 58 provided in the substrate transfer unit 62.

FIGS. 18A and 18B are diagrams schematically showing an orientation ofthe wafer W with respect to an incident direction of the ion beam B.FIG. 18A shows a state where the wafer W is inclined with respect to theincident direction of the ion beam B (z direction) and thus, a tiltangle θ which is not 0° is set. As shown in FIG. 18A, the tilt angle θis set as a rotation angle by which the wafer W is rotated around the xaxis. In a state where the tilt angle θ=0°, the ion beam B isperpendicularly incident into the wafer W. FIG. 18B shows a state wherethe wafer W is rotated around an axis which goes through a center O ofthe wafer W and is perpendicular to the wafer main surface, and thus, atwist angle φ which is not 0° is set. As shown in FIG. 18B, the twistangle φ is set as a rotation angle by which the wafer W is rotatedaround the axis perpendicular to the wafer main surface. In a statewhere the twist angle φ=0°, a line extending from the center O of thewafer W to an alignment mark M coincides with the y direction. Whendisposing the wafer W with respect to the ion beam B, appropriatelysetting the tilt angle θ and the twist angle φ can realize apredetermined channeling condition.

FIGS. 19A and 19B are diagrams schematically showing the wafer which isa target of the ion implantation process. FIG. 19A shows a crystalorientation of the wafer W, and FIG. 19B shows an atomic arrangement inthe vicinity of the surface of the wafer W. As the wafer W which is theimplantation target, a single crystal silicon substrate in which a planeorientation of the wafer main surface is the (100) plane can be used.The alignment mark M of the wafer W is provided at a position indicating<110> orientation.

FIGS. 20A to 20C are diagrams schematically showing a relationshipbetween the orientation of the wafer W and the atomic arrangement in thevicinity of the surface of the wafer W. FIGS. 20A to 20C are diagramsschematically showing the atomic arrangements in the vicinity of thewafer Wand show the atomic arrangements when viewed from the ion beam Bincident into the wafer W. In FIGS. 20A to 20C, positions of siliconatoms are indicated by black circles. In addition, the silicon atomspositioned at different positions in a depth direction (z direction) aredrawn in a xy plane in an overlapping manner.

FIG. 20A shows an atomic arrangement in a case where the atoms aredisposed to satisfy an axial channeling condition and shows a case wherethe wafer W is disposed in an orientation at the twist angle φ=23° andthe tilt angle θ=0°. In the shown axial channeling condition, aplurality of first crystal planes 96 formed of silicon atoms disposed onsolid lines and a plurality of second crystal planes 97 formed ofsilicon atoms disposed on broken lines cross each other to be disposedas a lattice, and thus, “axial channels” 95 are formed, which are axialclearances extending in one dimension along the direction in which theions are implanted. As a result, in the ion beam having an angulardistribution in at least one of the x direction and the y direction,only the ions traveling straight in the z direction causes thechanneling phenomenon, and the ions having angular components deviatedto some extent from the z direction are blocked by any crystal plane anddoes not cause the channeling phenomenon. Accordingly, the wafer Wdisposed to satisfy the axial channeling condition generates the “axialchanneling” which occurs on the ions traveling axially along theincident direction of the ion beam B.

The disposition which satisfies the axial channeling condition is notlimited to the above-described settings of the twist angle and tiltangle. Other twist angles and tilt angles may be used as long as thewafer is disposed such that the atomic arrangement shown in FIG. 20A isrealized. In order to realize the axial channeling condition, forexample, the twist angle φ of the wafer W may be substantially in arange of 15° to 30°, and the tilt angle θ of the wafer may besubstantially 0°.

FIG. 20B shows an atomic arrangement in a case where the atoms aredisposed to satisfy a plane channeling condition and shows a case wherethe wafer W is disposed in an orientation at the twist angle φ=0° andthe tilt angle θ=15°. In the shown plane channeling condition, aplurality of crystal planes 99 are formed by silicon atoms arranged in ayz plane, and a “planar channel” 98 which are clearances having atwo-dimensional spread between the crystal planes 99 facing each otherin the x direction is formed. As a result, in the ion beam having anangular distribution in the x direction, only the ions travelingstraight in the z direction cause the channeling phenomenon, and theions having angular components deviated to some extent from the zdirection in the x direction are blocked by the crystal planes 99 anddoes not cause the channeling phenomenon. Meanwhile, the ion beam havingan angular distribution in the y direction are not blocked by thecrystal planes 99 and the channeling phenomenon occurs in the clearancesbetween the crystal planes 99. Accordingly, the wafer disposed tosatisfy the plane channeling condition mainly generates the “planechanneling” which occurs on the ions traveling along a reference planedefined by both the z direction which is along the incident direction ofthe ion beam B and the y direction. Therefore, when the wafer disposedto satisfy the plane channeling condition is irradiated with the ionbeam, direction dependency is generated, in which the ions having theangular components in the x direction does not cause the phenomenon andthe ions having the angular components in the y direction cause thechanneling phenomenon.

The disposition which satisfies the plane channeling condition is notlimited to the above-described settings of the twist angle and tiltangle. Other twist angles and tilt angles maybe used as long as thewafer is disposed such that the atomic arrangement shown in FIG. 20B canbe realized. In order to realize the plane channeling condition, forexample, the twist angle φ of the wafer W may be substantially 0° to45°, and the tilt angle θ of the wafer W may be substantially in a rangeof substantially 15° to 60°.

FIG. 20C shows an atomic arrangement in a where the atoms are disposedto satisfy an off-channeling condition and shows a case where the waferW is disposed in an orientation at the twist angle φ=23° and the tiltangle θ=7°. In the off-channeling condition, any channel which is a pathfor the traveling ions is not visible, and it appears that the siliconatoms are disposed without clearances in both the x direction and the ydirection. As a result, when the wafer disposed so as to satisfy theoff-channeling condition is irradiated with the ion beam, t theoff-channeling state is realized in which the channeling phenomenon doesnot occur regardless of whether or not the ions constituting the ionbeam have the angular components in the x direction or the y direction.

The disposition which satisfies the off-channeling condition is notlimited to the above-described settings of the twist angle and tiltangle. Other twist angles and tilt angles maybe used as long as thewafer is disposed such that the atomic arrangement shown in FIG. 20C canbe realized. More specifically, if the wafer W is disposed in such anorientation that low-order crystal planes such as the {100} plane, the{110} plane, and the {111} plane of the wafer intersect diagonally thereference trajectory of the ion beam, other angular conditions may beused. In order to realize the off-channeling condition, for example, thetwist angle φ of the wafer W may be substantially in a range of 15° to30°, and the tilt angle θ of the wafer W may be substantially in a rangeof 7° to 15°.

In the present embodiment, the axial channeling condition shown in FIG.20A can be used as the disposition of the wafer “satisfying apredetermined channeling condition”. In the disposition shown in FIG.20A, the tilt angle θ is 0°, and thus, even in a case where a thick maskis formed on the wafer surface, the ion beam B is incident into thedirection perpendicular to the wafer surface, and it is possible toaccurately implant the ions into the location corresponding to theopening portion of the mask. In addition, as an implantation process formanufacturing a semiconductor device, only the implantation processusing the axial channeling condition shown in FIG. 20A may be performed,or the implantation process using the plane channeling condition shownin FIG. 20B and/or the implantation process using the off-channelingcondition shown in FIG. 20C may be additionally combined and performed.

FIG. 21 is a flowchart showing a flow of an ion implantation methodaccording to the embodiment. First, the energy of the ion beam B withwhich the wafer W should be irradiated is adjusted (S10). For example,it is possible to adjust the energy of the ion beam B by controlling theoperation of the high energy multistage linear acceleration unit 14.Subsequently, the angular distribution of the ion beam B with which thewafer W should be irradiated is adjusted (S12). For example, it ispossible to adjust the angular distribution of the ion beam B bychanging the potentials Qx and Qy of the lens devices 32 a to 32 c inthe beam shaper 32. In this case, the angular characteristics of thebeam may be adjusted such that the spread of the angular distribution isequal to or less than the critical angle θ for the channelingcorresponding to the energy and the ion species of the ion beam B.

Next, the wafer W which is the implantation target is transferred intothe ion implantation chamber 60 and is fixed on the wafer holding device42, and the temperature of the wafer W is adjusted using the temperatureadjustment device 50 (S14). In this case, it is possible to heat or coolthe wafer W using the temperature adjustment device 50 such that thetemperature of the wafer W reaches a desired temperature. In a casewhere the implantation process is performed in the room temperature, orin a case where the temperature of the wafer W is already adjusted to bethe desired temperature, the wafer W may not be heated or cooled.Subsequently, the orientation of wafer W is adjusted using the twistangle adjustment mechanism 46 and the tilt angle adjustment mechanism 48such that a desired channeling condition is satisfied (S16). Thetemperature adjustment process of S14 and the orientation adjustmentprocess of S16 may be performed in reverse order, or may be performed inparallel.

Subsequently, the wafer W whose temperature and orientation are adjustedis irradiated with the ion beam B and the ion implantation process isperformed (S18). The temperature adjustment of the wafer W may beperformed in parallel while the ion implantation process of S18 isperformed, and for example, the wafer W may be irradiated with the ionbeam B while the wafer W is heated or cooled. In addition, the wafer Wmay be heated using power applied to the wafer W by the irradiation ofthe ion beam B. For example, in a case where the wafer W is implanted ata high temperature, the wafer W may be heated using the temperatureadjustment device 50 before the beam irradiation and may be heated usingthe power of the beam during the beam irradiation. The heating by thetemperature adjustment device 50 may be used in combination during thebeam irradiation, or the cooling by the temperature adjustment device 50may be used in combination in a case where the wafer W is excessivelyheated using the power of the beam. In addition, the temperature of thewafer W may be maintained constantly during the beam irradiation underthe cooling by the temperature adjustment device 50, in order tosuppress the heating by the power of the beam.

Subsequently, if an additional irradiation with the ion beam B isnecessary (Y in S20), the processes in S10 to S18 are performed again.For example, as shown in FIGS. 11A to 11C and 12A to 12C, in the casewhere a plurality of implantation processes are performed by changingthe energy of the ion beam B and/or the temperature T of the wafer W,the processes in S10 to S18 are performed by changing the implantationcondition at each time. In this case, the changed implantationconditions may include the ion species, the energy, the dose, theangular distribution of the ion beam B, the tilt angle θ, the twistangle φ, the temperature T of the wafer W, or the like. Meanwhile, ifthere is no need for the additional irradiation with the ion beam B (Nin S20), the present flow ends.

In the plurality of implantation processes, the conditions of the wafertemperature T may be set to be approximately the room temperature (27°C., 300K). The temperature conditions may be set such that the wafertemperatures T are equal to or lower than the room temperature in all ofthe plurality of implantation processes, and for example, thetemperature conditions may be changed in a range of −200° C. to 27° C.As a specific example, temperatures of about −196° C. (77K), −123° C.(150K), −73° C. (200K), −23° C. (250K), and 27° C. (300K) may be set.Meanwhile, the temperature conditions may be set such that wafertemperatures T are equal to or higher than room temperature in all ofthe plurality of times of implantation processing, and, for example, thetemperature conditions may be changed in the range of 27° C. to 500° C.As a specific example, temperatures of about 27° C. (300K), 127° C.(400K), 227° C. (500K), 327° C. (600K), 427° C. (700K), 500° C. (773K)maybe set. In addition, temperatures both below the room temperature andabove the room temperature maybe included, and the temperatureconditions may be changed in a range of −200° C. to 500° C.

In the plurality of implantation process, the implantation profile maybe controlled by not only adjusting the wafer temperature T but also theangular distribution of the ion beam B, and at least one of an averagevalue (average angle) and a standard deviation value(divergent/convergent angle) of the angular distribution of the ion beamB may be finely adjusted. For example, in the plurality of implantationprocess, the average value of the angular distribution of the ion beam Bwith respect to the crystal axis C of the wafer W may be changed by 0.1°or more within a range less than the critical angle θ or more than thecritical angle θ_(c), and as a specific example, the average value maybe set to be 0.1°, 0.3°, 0.5°, 0.8°, 1°, 1.5°, 2°, 2.5°, 3°, 3.5°, 5°,7°, or the like. The average value of the angular distribution withrespect to the wafer W can be adjusted by the tilt angle adjustmentmechanism 48. The standard deviation value of the angular distributionof the ion beam B may be adjusted in 0.1° steps. The standard deviationvalue of the angular distribution of the ion beam B can be adjusted bythe beam shaper 32.

Moreover, in a case where the plurality of implantation processes areperformed with changing the energy of the ion beam B and the temperatureT of the wafer W, the plurality of implantation process may not becontinuously performed on one wafer W. For example, in a case where theplurality of implantation process using the same conditions areperformed on a plurality of wafers W for mass production, a firstimplantation process using a first condition maybe continuouslyperformed on the plurality of wafers, and thereafter, the setting of theion implanter 100 may be changed from the first condition to a secondcondition, and a second implantation process using the second conditionmay be continuously performed on the plurality of wafers.

In addition, the process of adjusting the temperature of the wafer W maybe performed in the middle of the transfer process of the wafer W. Forexample, as explained with FIG. 17 , it is necessary to move the waferW′ loaded into the ion implantation chamber 60 from theloading/unloading position to the implantation position by operation ofthe platen driving unit 40. It is also necessary to adjust the tiltangle θ and the twist angle φ for the wafer W disposed at theimplantation position. By heating or cooling the wafer W to a desiredtemperature during the performance of such a preparation process in theion implantation chamber 60, an additional operation time required forthe temperature adjustment can be reduced, and thus, it is possible toprevent throughput of the ion implantation process from decreasing.

In addition, the process of adjusting the temperature of the wafer W maybe performed in the preliminary chamber different from the ionimplantation chamber 60. For example, the substrate transfer unit 62 maybe provided with the preliminary chamber to control the temperature ofthe wafer W, and the wafer W may be heated or cooled using a temperatureadjustment device installed in the preliminary chamber. The substratetransfer robot 58 or the like may be provided with the temperatureadjustment device, and the substrate transfer robot 58 may be capable ofheating or cooling the wafer W during the transfer of the wafer W. Thewafer W may be heated or cooled only at a place different from the ionimplantation chamber 60, or the temperature control of the wafer W atthe place different from the ion implantation chamber 60 and thetemperature control in the ion implantation chamber 60 may be combinedwith each other. Moreover, instead of actively cooling the wafer W usingthe temperature adjustment device 50, the temperature of the wafer W maybe adjusted by cooling the wafer W using heat dissipation from the waferW due to the temperature difference between the wafer and a surroundingenvironment of the wafer.

It should be understood that the invention is not limited to theabove-described embodiment, but may be modified into various forms onthe basis of the spirit of the invention. Additionally, themodifications are included in the scope of the invention.

In the above-described embodiment, the case where the isolationimplantation or the photodiode implantation is performed by irradiatingthe wafer W with the ion beam B from above the mask 80 having a largethickness t is described as an example. The present embodiment is notlimited to the application described above, and, for example, thepresent embodiment may be applied to a formation of a trench-type pnjunction structure used in a power device or the like, a formation of atrench-type pn junction structure or a planar-type pn junction structureused in a logic circuit or the like, or the like. In this case, the ionimplantation maybe performed using an electrode layer, an insulatinglayer, or the like provided on the wafer surface as the mask.

In the above-described embodiment, the control of the implantationprofile of the implanted ions is described. The present embodiment canbe similarly applied to a control of profile of implantation damage(crystal defect) in the wafer caused by the ion implantation.

What is claimed is:
 1. An ion implantation method comprising: setting,by a temperature adjustment device, a temperature of a wafer to a firsttemperature; irradiating, by an ion implanter when the wafer is at thefirst temperature, a first ion beam onto a predetermined position on thewafer with an orientation at an implantation angle condition so as toform a first implantation profile in the wafer; setting, by thetemperature adjustment device after the ion implanter irradiates thefirst ion beam onto the wafer, the temperature of the wafer to a secondtemperature that differs from the first temperature; and irradiating, bythe ion implanter when the wafer is at the second temperature, a secondion beam onto the predetermined position on the wafer with theorientation at the implantation angle condition so as to form a secondimplantation profile in the wafer, wherein the first ion beam isadjusted by a beam shaper of the ion implanter such that the first ionbeam has a first angle distribution, wherein the second ion beam isadjusted by the beam shaper such that the second ion beam has a secondangle distribution, and wherein the first angle distribution and thesecond angle distribution satisfy a condition that at least a full widthat half maximum component of an angle distribution of an ion beamirradiated to the wafer is on-channeling, when the ion beam isirradiated onto the wafer at the predetermined position on the wafersurface in an incident direction under the implantation angle condition.2. The ion implantation method according to claim 1, wherein the firstimplantation profile is deeper in the wafer than the second implantationprofile.
 3. The ion implantation method according to claim 1, wherein awidth of the first implantation profile in an in-plane direction isdifferent from a width of the second implantation profile in thein-plane direction.
 4. The ion implantation method according to claim 3,wherein a width of the first implantation profile in the in-planedirection is smaller than a width of the second implantation profile inthe in-plane direction.
 5. The ion implantation method according toclaim 3, wherein a width of the first implantation profile in thein-plane direction is larger than a width of the second implantationprofile in the in-plane direction.
 6. The ion implantation methodaccording to claim 1, wherein the second temperature is higher than thefirst temperature.
 7. The ion implantation method according to claim 1,wherein the second temperature is lower than the first temperature. 8.The ion implantation method according to claim 1, wherein the firsttemperature and the second temperature are respectively between −200° C.and 500° C.
 9. The ion implantation method according to claim 1, whereina difference between the first temperature and the second temperature is100° C. or more.
 10. The ion implantation method according to claim 1,wherein an energy of the second ion beam is lower than an energy of thefirst ion beam.
 11. The ion implantation method according to claim 1,wherein an ion species of the first ion beam is a same species as an ionspecies of the second ion beam.
 12. The ion implantation methodaccording to claim 1, wherein an energy of the first ion beam isdifferent from an energy of the second ion beam.
 13. The ionimplantation method according to claim 1, wherein the first ion beam andthe second ion beam are respectively at a dose of 1×10¹⁴ cm⁻² or less,or 1×10¹³ cm⁻² or less.
 14. The ion implantation method according toclaim 1, wherein a divergent beam is from the group consisting of thefirst ion beam and the second ion beam.
 15. The ion implantation methodaccording to claim 1, wherein a convergent beam is from the groupconsisting of the first ion beam and the second ion beam.
 16. The ionimplantation method according to claim 1, further comprising:separating, during an irradiation of a beam from the group consisting ofthe first ion beam and the second ion beam, the temperature adjustmentdevice from a wafer holding device.
 17. The ion implantation methodaccording to claim 1, further comprising: irradiating, by the ionimplanter when the wafer is at a third temperature, a third ion beamonto the wafer at the implantation angle condition so as to form a thirdimplantation profile in the wafer.
 18. The ion implantation methodaccording to claim 17, wherein the third temperature differs from thefirst temperature.
 19. The ion implantation method according to claim17, wherein the second temperature differs from the third temperature.20. The ion implantation method according to claim 17, furthercomprising: setting, by the temperature adjustment device after the ionimplanter irradiates the second ion beam onto the wafer, the temperatureof the wafer to the third temperature.
 21. The ion implantation methodaccording to claim 1, wherein the temperature adjustment devicecomprises: a first temperature adjustment device that adjusts thetemperature of the wafer to the first temperature, and a secondtemperature adjustment device that adjusts the temperature of the waferto the second temperature.
 22. The ion implantation method according toclaim 1, wherein the first angle distribution is adjusted by focusing ordiverging the first ion beam in a first direction perpendicular to adirection of incidence of the ion beam to the wafer surface, and byfocusing or diverging the first ion beam in a second directionperpendicular to both the direction of incidence of the ion beam and thefirst direction, and wherein the second angle distribution is adjustedby focusing or diverging the second ion beam in a first direction and byfocusing or diverging the second ion beam in the second direction. 23.The ion implantation method according to claim 1, wherein the absolutevalue of the incident angle in the ion beam for on-channeling is smallerthan critical angle θ_(C) shown by the following expression (1)θ_(C)=√{square root over (Z₁Z₂ e ²/2πε₀E₁ d)}  (1) where Z1 is an atomicnumber of the implanted ion, Z2 is an atomic number of a material whichis an implantation target, El is energy of the implanted ion, and d isan atomic interval in a crystal of the material which is theimplantation target.